The invention relates generally to hydraulic controls for regulating the flow of hydraulic fluid to hydraulic actuators. More particularly, it relates to spool valves for regulating such flow.
Hydraulic valves for controlling the movement and position of hydraulic actuators that are connected to large loads usually include several hydraulic circuit protection devices necessary to prevent damage to the hydraulic system, either the actuator or the hydraulic valves themselves. The two primary problems faced by hydraulic systems are that a sudden impact on the actuator or a sudden application of high pressure hydraulic fluid may lead to a large high pressure pulse in hydraulic components that are not sized to handle these high pressure pulses. To cure this problem, hydraulic controls and particularly spool valves that are commonly used to regulate hydraulic flow are equipped with an over-pressure relief circuit that dumps excess pressure back to the hydraulic tank, which is at a substantially lower pressure than the hydraulic supply pressure. Typical tank pressures range from 0 to 100 psi, where typical supply pressures may range from 500 to 4,000 psi. The relief valve, by opening, permits fluid pressure applied to the actuator to be automatically reduced. Once the pressure is within the proper range, typically 100 to 800 psi, these over-pressure relief valves automatically close.
Another problem faced by hydraulic systems is the formation of a vacuum in hydraulic lines. Just as hydraulic over-pressure can damage hydraulic systems by bursting actuators, valves and conduits, a vacuum in a hydraulic line can cause the hydraulic fluid to vaporize. These vapor bubbles in themselves are not damaging. When the pressure is increased, however, these bubbles collapse upon themselves as the hydraulic vapor condenses. There are substantial local transient pressure waves produced. Pressure waves formed by the collapsing bubbles will, over time, damage and dangerously weaken the hydraulic components in the system. This problem is called xe2x80x9ccavitationxe2x80x9d.
For this reason, hydraulic controls, and particularly hydraulic spool valves and valve bodies, are provided with xe2x80x9canti-cavitation valvesxe2x80x9d. These valves operate in a somewhat similar fashion to over-pressure relief valves. In a sense, anti-cavitation valves are under-pressure relief valves. When a hydraulic pressure drops below tank (or xe2x80x9creturnxe2x80x9d) pressure, the anti-cavitation valves automatically open and permit the flow of hydraulic fluid into the low pressure regions, thus preventing the formation of hydraulic vapor bubbles. When the under-pressure condition is relieved, the anti-cavitation valves automatically close, thereby cutting off additional hydraulic flow.
Another common feature in hydraulic controls, spool valves and valve bodies is the hydraulic check valve. A check valve is one that permits the flow of fluid in one direction only. These valves are typically disposed between a manually or electrically actuated spool (that direct flow to an actuator) and the actuator itself. Check valves relieve the pressure differential that would otherwise remain on the spool at all times. Without the check valve, sudden over-pressure conditions in the actuator would be instantly transmitted backwards to the control valve that regulates flow to or from the cylinder. These sudden pressure pulses can cause the control valve (the directional spool valve) damage. In addition, the check valves reduce leakage that would otherwise occur if the actuator pressure was maintained on the spool.
In prior art spool valves, these three valves: check valve, anti-cavitation valve and over-pressure relief valve, typically required that three different openings be drilled into the valve body, one for each valve. This required extensive machining. Typically, the valve body was drilled at three different locations.
What is needed, therefore, is a new check valve, over-pressure relief valve, and anti-cavitation valve arrangement that reduces the required or typical number of holes in a valve body. It is an object of this invention to provide such a valve arrangement.
In accordance with the first embodiment of the invention, a unitary insert for a cavity in a valve body is disclosed that includes a check valve, an anti-cavitation valve, and a pressure relief valve. The insert may have a longitudinal axis, a first end and a second end, and the first end may include a circular sealing surface coaxial with the longitudinal axis and configured to engage a mating coaxial circular sealing surface defined on an inner surface of the valve body cavity. The anti-cavitation valve may also include a first pair of coaxial mating surfaces defining therebetween a first flow path that opens under cavitation conditions. The pressure relief valve may include a second pair of coaxial mating surfaces that define therebetween a second flow path that opens under over-pressure conditions. The anti-cavitation valve may include an anti-cavitation spring disposed to bias the first pair of mating surfaces together. The pressure relief valve may include a relief spring disposed to bias the second pair of mating surfaces together. The first and second springs may be coaxial.
In accordance with the second embodiment of the invention, a valve for directing the flow of fluid both to and from a hydraulic actuator is disclosed including: a valve body having a first cavity configured to receive a valve insert, the first cavity having a cylindrical inner surface and a bottom; an insert disposed in the first cavity, the insert including an anti-cavitation valve, a check valve and a pressure relief valve; and a spool disposed in the valve body and configured to direct the flow of hydraulic fluid both from a source of hydraulic supply to an outlet port, and from the outlet port to a hydraulic tank. The insert may be disposed within the valve body to move axially within the cavity, and by such motion to function as the check valve. The insert may include a shell and a valve assembly inside the shell, wherein the valve assembly is disposed to move axially with respect to the shell, and by such motion to reduce cavitation at the outlet. The valve assembly may include a poppet and a poppet seat, and the poppet may be disposed to move with respect to the poppet seat to function as the pressure relief valve. The anti-cavitation valve may include a first seat disposed on an inner surface of the insert body and a second seat disposed on an annular ring of a valve assembly disposed within the insert body and configured to seal against the first seat. The valve assembly may include a poppet having a third seat wherein the annular ring has a fourth seat and the third and fourth seats are disposed to seal against each other. A first spring may be provided to move the insert axially to function as a check valve. The valve may also include a second spring disposed within the insert body to move the valve assembly axially within the insert body such that the first and second seats are sealed against each other. The valve assembly may also include a third spring disposed to bias the poppet""s third seat against the annular ring""s fourth seat.
In accordance with the third embodiment of the invention, a bi-directional hydraulic flow control valve that is couplable to a supply of pressurized hydraulic fluid and a hydraulic drain or tank, includes: a valve body with an elongate opening, two cavities, and two outlet ports; a valve spool with a plurality of lands positioned within the elongate opening and fluidly communicating with the first and second outlet ports and the hydraulic supply and the tank, such that axially moving the spool from a first neutral position to a first fill position will direct a flow of hydraulic fluid from the first outlet port to the tank and from the hydraulic supply to the second output port, and further where moving the spool from the neutral position to a second fill position will direct the flow from the hydraulic supply to the first outlet port and from the second outlet port to the tank; a first insert disposed in the first cavity and in fluid communication with the first outlet port, the first insert including a check valve, an anti-cavitation valve and a pressure relief valve; and a second insert disposed in the second cavity and in fluid communication with the second outlet port, the second insert including a check valve, an anti-cavitation valve and a pressure relief valve. Each of the first and second inserts may include a hollow valve body having an internal valve assembly with a first pair of seats in a mutually sealing arrangement to prevent or permit the flow of sufficient hydraulic fluid to prevent cavitation in a cavitation condition, and a second pair of seats in a mutually sealing arrangement to prevent or permit the flow of sufficient fluid to relieve an over-pressure condition. The valve assemblies inside the hollow valve bodies may each include first and second springs configured to close the first and second pair of seats, respectively, when the respective cavitation condition and the over-pressure condition no longer exist. Each of the first and second inserts may include a check valve seat located on an outside surface of the insert that abuts and seals against a mating valve seat on an inner surface of the first and second cavities, respectively. The valve may also include first and second check valve biasing springs abutting the first and second inserts, respectively, to bias the check valves of the first and second inserts closed. The first and second inserts may be disposed in flow paths between the first and second outlet ports and the spool to check hydraulic fluid from flowing backwards from the two outlet ports to the spool when the spool is in the neutral position.